Following the developments in different technological fields, more and more finely designed and high-power products have been introduced into the market. However, the high-power products would inevitably produce high temperature during the operation thereof to endanger the products. The electronic elements in the products might become burned-out to cause failed products or even more serious problems. Therefore, most of the precision products are provided with a cooling fan to force away the heat produced by the products during the operation thereof.
FIGS. 1A and 1B are exploded and assembled sectional views, respectively, of a conventional dual-bearing fan structure. As shown, the dual-bearing fan structure includes a fan frame 10 and a blade hub 11. The fan frame 10 is provided at a central portion with a base 101, which has an open end 102 and a closed end 103. A first bearing 12, a second bearing 13, and a spring element 14 are received in the base 101. A radially inward annular protrusion 104 is formed in the base 101, so that the first and the second bearing 12, 13 are separately located at two axially opposite sides of the annular protrusion 104.
The blade hub 11 has a rotary shaft 110, which has a proximal end embedded in the blade hub 11 and a distal end extended into the base 101 through the spring element 14 and the first and second bearing 12, 13 to project from the second bearing 13 into the closed end of the base 101. A stop ring 15 is connected to the distal end of the rotary shaft 110 in the closed end of the base 101, 50 as to hold the second bearing 13 in place in the base 101. The spring element 14 is put around the rotary shaft 110 and located above the first bearing 12 in the open end 102 of the base 101, such that two ends of the spring element 14 are tightly pressed against the blade hub 11 and the first bearing 12. When the dual-bearing fan operates, the first and the second bearing 12, 13 together radially support the blade hub 11 for the same to rotate, so that blades on blade hub 11 of the dual-bearing fan structure can be rotated rapidly.
The base 101 of the fan frame 10 is formed by injection molding. On injection molding, it is difficult to control the concentricity of the spaces in the base 101 at two axially opposite sides of the annular protrusion 104 for separately holding the first and the second bearing 12, 13. Therefore, when assembling the rotary shaft 110 of the blade hub 11 to the first and the second bearing 12, 13, it is uneasy to control the concentricity between the first and the second bearing 12, 13 and the perpendicularity of the inner bore of the base 101. As a result, when the fan structure operates, abnormal wearing tends to occur on the rotary shaft 110 and the first and second bearings 12, 13, which will produce noise and shorten the service life of the fan.
By providing two bearings to enable the fan structure to operation, the manufacturing cost of the fan will correspondingly increase. Moreover, for a super slim-type fan, there would not be sufficient space for two ball bearings. Therefore, the normal bearings must be replaced by ball bearings with smaller size to also increase the manufacturing cost of the fan.
In brief, the conventional dual-bearing fan structure has the following disadvantages: (1) increased manufacturing cost; (2) uneasy to control the concentricity between the two bearings when assembling the fan structure; (3) producing noise during operation; and (4) shortened service life.
It is therefore tried by the inventor to develop an improved single-bearing fan structure to overcome the problems in the conventional dual-bearing fan structure.